LTC3218 Datasheet, PDF (6/12 Pages) Linear Technology – 400mA Single Wire Camera LED Charge Pump

LTC3218
BLOCK DIAGRAM
CP
CM
1
9
OSCILLATOR
V_IN 10
ENT 4
ENF 7
VOLTAGE
CLAMP
CONTROL
LOGIC
MODE
CONTROL
V_REF
CURRENT
SOURCE
CONTROL
2 CPO
220mΩ
106Ω
3 I_LED
I_SETT
5
I_SETF
6
GND GND
8
11
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OPERATION
The LTC3218 uses a switched capacitor charge pump to
power a high current LED with a programmed regulated
current. Current regulation is achieved using an internal
current sense resistor connected between the CPO and
I_LED pins. The part starts up in 1x mode after a soft-start
period. In this mode, V_IN is connected to the CPO through
switches, the strengths of which are modulated to achieve
the desired LED current. This mode provides maximum
efficiency and minimum noise. The LTC3218 will remain in
this mode until the LED forward voltage (V_F) approaches
the maximum CPO voltage possible in this mode. When
this dropout condition occurs, the LTC3218 will switch to
2x mode after a soft-start period.
The current delivered to the LED load is controlled by the
internal programmable current source. The current is
programmed by resistors connected between the I_SETT
and I_SETF pins and GND. The resistor values needed to
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